Add the deprecated field to OpenAPI definitions and JSON Schemas (#1940)

I did a quick search of the "deprecated" word in the data folder and set the
field where the description says that a property is deprecated.

This does not change the rendering of the spec because the
descriptions already talk about the deprecation,
but it can be used by tools that rely on the OpenAPI definitions and JSON Schemas.

Signed-off-by: Kévin Commaille <zecakeh@tedomum.fr>

data/api/client-server/joining.yaml

@@ -139,6 +139,7 @@ paths:
             type: string
         - in: query
           name: server_name
+          deprecated: true
           x-changedInMatrixVersion:
             "1.12": |-
               This parameter has been deprecated in favour of `via` and will be removed in